There were a variety of causes, some cultural, some political, and some theological.
The Eastern areas of the Church used Greek as the language of the Church while the West used Latin. This lead to a certain divergence in thought, as Eastern writings were available only in translation or not at all. At the same time Western writers were, often, not available in the East at all. For Example, the works of Augustine were never translated into Greek. There were also differences in the liturgy and church practices which caused some tension. The Eastern practice of allowing clerical marriage was one example of the differing practices.
The Eastern Churches did not accept the the claims of supremacy made by the Pope. The Western Church did not accept the power the Byzantine Emperor exercised over the Eastern Church.
THe major theological issue was what is known as the "foliage" clause, an addition made to the Nicene Creed by the Western Church.
Many of these issues were long standing issues, and wear politely ignored. The excommunications of 1054 were not seen as causing a permanent schism at the time, but events of following centuries especially the sacking of Constantinople in the 4Th Crusade made the rift wider.